Sludge digester

Abstract

A sludge digester having a main tank in conjunction with a gas-holding cover is disclosed. The cover includes a roof and a depending sideskirt which telescopes in relationship to the main tank. Positioned at the bottom edge of the sideskirt are a multitude of ballast members. A chamber, adapted to contain a quantity of liquid, is associated with the main tank. The sideskirt and the ballast members are submerged within the liquid contained within the chamber to form a gas tight seal of the cover with the main tank. The chamber also includes a system for maintaining a predetermined liquid level in the chamber dependent on the position of the ballast members in the chamber.

We claim: 
     
       1. A ballasted, gas-holding, liquid sludge digester comprising: a main liquid sludge tank having a bottom wall and upwardly projecting sidewall;   a cover having a top and depending sideskirt structure which telescopes with respect to the upwardly projecting sidewall of the main tank;   ballast supported near the lower edge of said sideskirt;   a ballast-engaging, liquid-containing well joined to said sidewall of said main tank such that said cover provides a gas-tight seal when said ballast interacts with liquid in said well so as to be partially emerged or fully submerged in the liquid;   liquid fill means interacting with said well to maintain a predetermined liquid level in the well when said ballast is at least partially emerged from the liquid in said well; and   overflow means interacting with said well to maintain a predetermined liquid level in the well when said ballast is submerged in the liquid in the well.   
     
     
       2. The digester of claim 1 wherein said well circumscribes said main liquid sludge tank. 
     
     
       3. The digester of claim 1 wherein said overflow means is in a fixed relationship to said well. 
     
     
       4. The digester of claim 1 wherein said liquid fill means has liquid level sensing means to determine the level of liquid in said well.